Prior to the advent of fly-by-wire technology, flight control surfaces on a commercial aircraft were controlled using a complex system of cables and mechanical controls. Since the advent of fly-by-wire technology, such mechanical control systems were replaced with systems having no direct mechanical couplings between pilot controls and flight control surfaces. Instead of using mechanical couplings such as cables, a fly-by-wire system including pilot control transducers senses the position of the pilot controls and generates electrical signals proportional to the position of the pilot controls. The electrical signals are combined with other airplane data in a primary flight computer to produce a flight control surface command that controls movement of the flight control surfaces of the aircraft.
Because safety is always a high priority in the aircraft industry, a fly-by-wire system usually includes redundant components so that if one component of the system fails, a pilot can still safely control the aircraft. An example of such a fly-by-wire system is described in commonly assigned U.S. patent application Ser. No. 07/893,339, entitled Multi-Access Redundant Fly-By-Wire Primary Flight Control System, to Buus, filed Jun. 3, 1992, the disclosure and drawings of which are specifically incorporated herein by reference. The described fly-by-wire system is divided into a series of independent control channels wherein each control channel within the system is substantially isolated from the other control channels. Consequently, a data error value occurring in one channel does not affect the continued operation of the remaining channels such that a pilot can fly the aircraft using only one channel.
This example of a fly-by-wire system includes many other redundant systems to ensure the continuous smooth operation during flight. For example, this system includes autopilot flight director computers, air data modules, engine indication and crew alerting systems, airplane information management systems, etc. The independent control channels are in direct communication with these aircraft systems via a global communications data bus. However, each component of the fly-by-wire system, including the global communication data bus, may represent a potentially weak link that might introduce a problem in the event of failure of that component or in the event of a broken or loose connection to that component.
To this end, fly-by-wire architectures for the Boeing 777 have been developed with an asynchronous multi-channel system (that includes a minimum of three channels with a minimum of three computation lanes in each channel) as the host to serve as guardian of common communication media. Three computation lanes in each channel employ dissimilar processors and compilers so that the computer architecture is fail-operational to generic errors. However, these systems are expensive because of their reliance on hardware solutions.
Consequently, there is a need to provide fly-by-wire systems with the ability to monitor and identify failures or faults in aircraft components efficiently and economically.